The term “proppant” is indicative of particulate material which is injected into fractures in subterranean formations surrounding oil wells, gas wells, water wells, and other similar bore holes to provide support to hold (prop) these fractures open and allow gas or liquid to flow through the fracture to the bore hole or from the formation. Uncoated and/or coated particles are often used as proppants to keep open fractures imposed by hydraulic fracturing upon a subterranean formation, for example, an oil or gas bearing strata, and provide a conductive channel in the formation.
Fracturing of the subterranean formation is conducted to increase oil and/or gas production. Fracturing is caused by the injection of a fluid, for example, one or more of a hydrocarbon, water, foam or emulsion, into a formation at a rate that exceeds the formation's ability to accept the flow. The inability for the formation to dissipate the fluid results in a buildup of pressure. When this pressure buildup exceeds the strength of the formation rock, a fracture is initiated. Continued pumping of the fracturing fluid will result in the fracture growing in length, width and height. The rate required to initiate and extend the fracture is related to the injection rate and viscosity of the fracturing fluid.
The fracturing process also includes placing a particulate material, referred to as a “proppant material”, “propping agent” or “proppant” in the formation to maintain the fracture in a propped condition when the injection pressure is released by resisting forces tending to close the fracture. As the fracture forms, the proppants are carried into the fracture by suspending them in a fracturing fluid or additional fluid or foam to fill the fracture with a slurry of proppant. Upon ceasing the injection of fluid, the proppants form a pack that serves to hold open the fractures. The propped fracture thus provides a highly conductive channel for the production of hydrocarbon and/or recovery of fracturing process water from the formation.
However, it has been well recognized in the oilfield hydraulic fracturing industry that production of high volumes of water causes problems such as corrosion of tubulars, fines migration, hydrostatic loading and cessation of hydrocarbon production when wells must be shut in. The production of water also leads to increased production costs as the produced water must be treated and disposed of safely.
Further, attempts at addressing these issues have been less than successful. Undesirable water production has been attempted to be controlled by 1) conformance control by using polymeric gels and resins such as polyacrylamide and polyphenolics; 2) physical barriers such as cement or casing patches; 3) use of chemicals to change the formation relative permeability to promote hydrocarbon flow over water flow; and 4) use of an injection well/fluid injection to mitigate the pressure gradient formed when producing the hydrocarbons. However, these water treatment approaches are generally lacking in that they result in complete shut-off when applied and decrease the flow of hydrocarbons as well as water. Additionally, directed placement is difficult and the relative permeability of the reservoir for gas or oil is often adversely affected.
Accordingly, there is a need for a proppant material which can be readily handled during surface operations and pumped downhole to hinder intrusion of unwanted water into the generated fracture, while simultaneously promoting or maintaining the flow of hydrocarbon through a proppant pack.